Nocathiacin is a type of novel agent against multi-drug resistant bacteria, which is isolated from a soil microorganism and has novel structure and significant antibacterial activity. It is one of those thiopeptide antibiotics showing most potential in clinic application (see: J. Antibiot. 2003, 26:232-242). As a common characteristic of the thiopeptide antibiotics, the nocathiacin has a special high-hydrophobic ring system similar to other antibiotics in the same group, which possesses an extremely poor water solubility. In order to improve the water solubility of nocathiacin, a great number of series chemical and biological modification and transformation studies direct to the hydroxyl groups on the dehydroalanine side chain, indole and pyridyl rings of nocathiacin have been conducted, which are all failed due to such factors as complicated preparation and safety issues (see: J Org Chem, 2002, 67(24):8699-8702; J Nat Prod, 2005, 68(4):550-553; Bioorg Med Chem Lett, 2004, 14(14):3743-3746).
However, it is reported in literatures that nocathiacin possesses super-strong antibacterial activities against most gram-positive bacteria, particularly methicillin-resistant staphylococcus aureus (MRSA), penicillin-resistant streptococcus pneumoniae (PRSP), vancomycin-resistant enterococcus (VRE) and mycobacterium tuberculosis with effective concentration in a level less than 1 μg/ml; (see: J. Antibiot. 2003, 56:226-231). This shows that nocathiacin in clinic can be implemented by using low dose of nocathiacin. For the medicines with low doses in clinical application, the problem of low solubility could be relatively feasible to be solved through a pharmaceutical preparation because of the ease of increasing the solubility to a small degree with various approaches, and this problem may not become a key factor to limit its clinic application. On the other hand, as a cyclopeptide compound, the stability of nocathiacin is a major obstacle to be overcome for pharmaceutical usefulness. Therefore, the combination of solving the issues on both solubility and stability is challenging, which requires extensive investigation.
The Chinese patent (application No.: 201010548129.8) under the title of “Nocathiacin Antibiotic Drug Composition Containing Emulsifying Agent” discloses a drug composition containing nocathiacin and a drug carrier, and further includes a water-soluble emulsifying agent and a lipophilic emulsifying agent, wherein the drug carrier is composed of an aqueous phase and an organic phase. The Chinese patent (application No.: 201010548142.3) under the title of “Drug Composition of Nocathiacin Antibiotics Containing Lipid Material” discloses a drug composition containing nocathiacin antibiotics, which mainly includes the principal drug nocathiacin and the lipid material, wherein the lipid material is selected from phospholipid or cholesterol. And the Chinese patent (application No.: 201010548134.9) under the title of “Drug Composition Containing Nocathiacin Antibiotics” specifically discloses a drug composition containing nocathiacin antibiotics, which includes nocathiacin, a drug carrier and a hydrotropic substance, wherein the hydrotropic substance is selected from latent solvent or solubilizer; and the drug carrier is a physiologically dissolving medium with a pH of 4-9. Different preparations are respectively used in the above-mentioned patents to improve the solubility of nocathiacin. However, all the above-mentioned patents relate to liquid preparations of nocathiacin, which only address the poor solubility of nocathiacin, but do not deal with the stability of nocathiacin. As a thiopeptide compound, nocathiacin is sensitive to various environmental factors such as moistness, heat, light and the like, and is easy to degrade; therefore, it is very necessary to obtain a stable pharmaceutical agent containing nocathiacin while improving the solubility of nocathiacin at present.
There are multiple factors that affect the activity of protein or peptide drugs, which mainly include two aspects, wherein one aspect refers to structural factors including molecular weight, amino acid composition, amino acid sequence, presence of disulfide linkage, position of disulfide linkage, and 3-dimensional structure; the second aspect refers to peripheral environmental factors of the macromolecules, where changes like coagulation, precipitation, hydrolysis and deamidating will occur to the proteins or peptides due to the influences of complicated physical and chemical factors. Lyophilization refers to a drying method of freezing the drugs under a low temperature, lyophilizing the drugs under a vacuum condition to remove crystal ice, and performing desorption drying to remove partial bound water after the ending of sublimation. The lyophilizing technology can keep the activity of proteins and peptides for a long term because of the moderate condition and lower moisture content in the finished products. Therefore, lyophilized preparations are mostly applied to protein or peptide drugs.
Compared with other preparation methods, the lyophilization has the following advantages:
1) the liquid pharmaceutical formulation is sub-packed conveniently and accurately before lyophilizing, so that continued production can be achieved; 2) the processing condition is moderate, and drying is performed under low temperature with low pressure, which is beneficial for keeping the activity of temperature-sensitive substances, and can avoid the decomposition and degeneration under high temperature and high pressure, so that the drugs will not be denatured; 3) the moisture content is low, where the moisture content of the lyophilized product is generally 1%-3%; meanwhile, the product can be even dried and stored in case of nitrogen gas protection in vacuum, and cannot be easily oxidized, thus being beneficial for long distance transportation and long term storage; 4) the product has an excellent appearance, which is a porous loose structure and the color does not change substantially, and the rehydration characteristics are good, enabling the lyophilized drugs to absorb water quickly so as to be reduced to a state before being lyophilized; and 5) a lyophilizing device is operated closely, and the installation environment has high cleanness, which reduces the possibility of contamination by microorganisms, particulate, dry and neutralize anoxia after packing, and can play the roles of sterilizing and suppressing bacterial viability.
However, when the lyophilized preparation is applied to the peptide and protein drugs, requirements on selecting accessories are very strict; and inappropriate selection of the accessories will cause instability of the product to result in the loss of activity. Moreover, a solvent for preparing the liquid pharmaceutical formulation before lyophilizing cannot be selected randomly, and is only limited to water or organic solvents having higher freezing point. Sometimes, a turbidness phenomenon will occur to the lyophilized product while re-dissolving it, and this has to be considered and researched by experiments for developing the lyophilized preparation.
At present, no studies on lyophilized pharmaceutical agent containing nocathiacin and its stability have been reported in literatures.